1. Field of the Invention
The present invention relates to a stator of a brushless direct current motor and a method for making it, wherein the stator of the brushless direct current motor may be processed and manufactured conveniently.
2. Description of the Related Art
A conventional stator combination structure of a miniature heat-sink fan in accordance with the prior art shown in FIG. 1 comprises a stator coil 90, upper and lower pole plates 91 and 92, a circuit board 93, and a housing 94. A metallic shaft tube 95 having a proper outer diameter passes through central holes of the stator coil 90, the upper and lower pole plates 91 and 92, and the circuit board 93, so that they are combined integrally. Then, the bottom of the metallic shaft tube 95 is pressed in the central column hole 96 of the housing 94. The outer diameter of the metallic shaft tube 95 is provided with multiple sections, and has a top end formed with an annular lip 951, a mediate portion formed with an enlarged diameter portion 952, and a bottom 953. The stator coil 90 is provided with a central hole having a diameter slightly greater than the outer diameter of the enlarged diameter portion 952 of the metallic shaft tube 95. The upper pole plate 91 is provided with a central hole having a diameter slightly smaller than the outer diameter of the annular lip 951 of the metallic shaft tube 95. The lower pole plate 92 is provided with a central hole having a diameter slightly smaller than the outer diameter of the bottom 953 of the metallic shaft tube 95. The circuit board 93 is provided with a central hole having a diameter slightly smaller than the outer diameter of the bottom 953 of the metallic shaft tube 95. The upper pole plate 91 is pressed on the annular lip 951 of the metallic shaft tube 95 in a forcibly press manner. Then, the stator coil 90 is mounted on the enlarged diameter portion 952 of the metallic shaft tube 95 through the bottom 953 of the metallic shaft tube 95. Then, the lower pole plate 92 and the circuit board 93 are pressed on the bottom 953 of the metallic shaft tube 95, so that the stator coil 90 is clamped by the upper and lower pole plates 91 and 92 to be fixed on the enlarged diameter portion 952 of the metallic shaft tube 95 by the diameter difference of the outer diameter of the metallic shaft tube 95. The outer diameter of the bottom 953 of the metallic shaft tube 95 is slightly greater than the inner diameter of the central column hole 96 of the housing 94.
In such a stator of the conventional brushless direct current motor, the metallic shaft tube 95 needs to be formed with three sections of different diameters, and the upper and lower pole plates 91 and 92 and the circuit board 93 need to be respectively formed with an inner hole whose inner diameter forms a proper tolerance with the outer diameter of the metallic shaft tube 95. Thus, fabrication of the stator is more inconvenience. In addition, the upper and lower pole plates 91 and 92 each only have a smaller thickness. Thus, the sensing area of the upper and lower pole plates 91 and 92 and the rotor is reduced relatively. Thus, the stator cannot enhance the rotational torque of the rotor.
The stator structure of another conventional brushless direct current motor in accordance with the prior art shown in FIG. 2 comprises a stator 80 wound with a coil 803. The upper and lower ends of the stator 80 are provided with columns 801 and 802 for combining and positioning the upper and lower pole plates 81 and 82 and the circuit board 83. A metallic shaft tube 84 whose outer diameter is greater than the diameter of the central holes respectively provided by the stator 80, the upper and lower pole plates 81 and 82 and the circuit board 83, may be pressed into the central holes in a forcibly press manner. The metallic shaft tube 84 has a protruding annular lip 841 to prevent detachment, and the rotation shaft 851 of the rotor 85 may be pivoted on the metallic shaft tube 84 to rotate. In such a stator of the conventional brushless direct current motor, the fabrication also uses the difference of the larger and the smaller diameters to combine in a forcibly press manner, and also needs combination of the columns 801 and 802 provided by the upper and lower ends of the stator 80 with the upper and lower pole plates 81 and 82 and the circuit board 83. Thus, the fabrication of the stator is more inconvenience. In addition, the upper and lower pole plates 81 and 82 each only have a smaller thickness. Thus, the sensing area of the upper and lower pole plates 81 and 82 and the annular permanent magnet 852 of the rotor 85 is small. Thus, the stator cannot enhance the rotational torque of the rotor.
The primary objective of the present invention is to provide a method for making a stator of a brushless direct current motor, wherein the stator may be processed and manufactured conveniently.
A secondary objective of the present invention is to provide a stator of a brushless direct current motor, wherein the upper and lower pole plates of the stator and the annular permanent magnet of the rotor may have a larger sensing area, and have a larger magnetically conducting passage. Thus, the stator may enhance the rotational torque of the rotor.
In accordance with the present invention, there is provided a method for making a stator of a brushless direct current motor, includes the steps of: winding a coil set to predetermined turns, thereby forming a ring body having a central hole, and performing an insulation process; mounting at least two pole plates on two end faces of the coil set respectively, the pole face and the magnetically conducting plates of each pole plate encompassing the inner and outer periphery of the coil set respectively, and a wiring head of the coil set being drawn outside of the pole plate; and mounting a combination member on the magnetically conducting rings (or plates) of each pole plate, thereby forming a stator. The pole faces of each pole plate may be induced with the permanent magnet of the rotor.
Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.